Liverpool maintained pressure on table-topping Manchester City with three second-half goals sealing a comfortable 3-0 victory at Watford on Saturday.

After a largely uneventful first half, Mohamed Salah put the ball past Watford goalkeeper Ben Foster in the 67th minute before England defender Trent Alexander-Arnold scored a stunning second goal.

The 20-year-old beat Foster with a brilliant whipped free kick from 25 metres nine minutes later, before his international team mate Jordan Henderson was dismissed for a second bookable offence.

Liverpool were not hindered by their numerical disadvantage, however, with Roberto Firmino adding a late third goal as the visitors extended their unbeaten start to the Premier League season to 13 games.

Jurgen Klopp's side remain second with 33 points and trail Champions City by two points after Pep Guardiola's men beat West Ham United 4-0 on Saturday. Watford slipped to ninth after a third game without victory.

Mohamed Salah celebrates putting Liverpool ahead. Getty

"They had big chances in the first half and we struggled to create chances but we persevered which is the good thing about this team this year," Alexander-Arnold told the Premier League.

"We are happy to come away with the three points. After the international break we have set a marker down and, hopefully, we will be able to build on that.

"A lot of people might look towards Manchester City and Chelsea games but every game is important and if you come away with draws when you feel like you should win, that is where you will go wrong.

"We have another massive game at the weekend [against cross-city rivals Everton.]"

In a blistering start to the season, Klopp's side had conceded just four goals in 12 games, but they were sent an early warning when Gerard Deulofeu had a goal disallowed for offside inside three minutes.

That early drama quickly fizzled out for the remainder of the first half, however, and with City leading handsomely at West Ham, Liverpool knew they needed to improve after the break.

Salah set them on their way, finishing a move which also involved Sadio Mane and Firmino.

Then, a week after registering his first international goal, Alexander-Arnold added a second with a sublime, curling free kick.

Henderson's dismissal with eight minutes left marred Liverpool's day before Firmino pounced late, after Mane had been denied, to seal another comfortable victory for Klopp's unbeaten side.